1. Field of the Invention
The present invention is related to the field of data networks. In particular, the present invention is related to an improved method and apparatus for transmitting data frames between nodes connected to a meshed data network having permanently interconnected switches.
2. Description of the Related Art
Traditional data networks include the Ethernet/IEEE 802.3 Local Area Networks (LAN) and IEEE 802.5 Token Ring LAN. These LANs comprise a connectionless oriented shared medium over which unicast and broadcast packets are transmitted. In contrast, an Asynchronous Transfer Mode (ATM) network comprises a connection oriented packet switched network.
Communication between nodes (e.g., workstations, servers, bridges, etc.) on separate LANs interconnected via an ATM network or between a node on the ATM network and a node on the LAN wherein the ATM network and LAN are interconnected by, e.g., one or more switches, has been accomplished by emulating the LAN in the ATM network so that, from the perspective of the nodes, the ATM network is transparent. This service is known in the data networking industry as LAN Emulation (LE) service over ATM. LE service supports the interconnection of ATM networks and LANs using traditional bridging methods and allows interoperability between applications on nodes, whether the nodes are connected to an ATM network or LAN.
FIG. 1 provides an example of a data network 100 comprising, e.g., an IEEE 802.3 LAN 120 and 130 interconnected via an ATM network 110. Connected via segment 160 to the ATM network 110 is an ATM-based node 170. Respectively connected to LANs 120 and 130 are LAN-based nodes 140 and 150. With LE service, node 140 can communicate with node 170 or 150 utilizing the IEEE 802.2 LLC, network and transport layer protocols that it would otherwise use in a strictly LAN environment.
LE service is provided for by one or more LAN Emulation (LE) Clients (LECs) and a LAN Emulation (LE) service comprising an LE Configuration Server (LECS), LE Server (LES), and a Broadcast and Unknown Server (BUS). Generally speaking, the LECS assigns LE clients to a particular emulated LAN, while the LES registers and resolves MAC addresses or source route descriptors to ATM addresses, and the BUS handles multicast packets and unicast packets with an unknown destination address.
An LE Client is an ATM node such as a switch or node identified by one or more Media Access Control (MAC) addresses. The LE Service may be centralized or distributed across a number of devices such as an ATM node or switch. LECs communicate with the LES via control or data Virtual Circuit Connections (VCCs). The VCCs may be either Switched Virtual Circuits (SVCs) or Permanent Virtual Circuits (PVCs). For example, if the data network 100 of FIG. 2 supported LE service, switches 210 and 230 may well operate as LECs, while switch 220 may perform the function of the LES.
Communication between LECs and the LES is defined according to the LAN Emulation User to Network Interface (LUNI). LUNI provides for, among other things, initialization of LE Clients, registration of MAC addresses represented by the LECs, ATM to MAC Address Resolution Protocol (LE-ARP), and transferring data from an LE Client to another LE Client as part of the LE service.
A LEC has a separate VCC for transmission of control packets such as LE-ARP packets and for data packets such as IEEE 802.3 frames. Thus, at least one separate VCC exists between the LEC and each component of the LES, namely, the LECS, the LEC, and the BUS, and in fact, in some instances, two VCCs exist between the LEC and LES component. Given communication occurring between two nodes in the network 100, multiple control packets must be transmitted between the LEC and LES as well as the data packet(s) transmitted between the nodes. What is needed is a method and apparatus by which nodes in a network utilizing LE service may communicate more efficiently, without the need for transmission of multiple control packets between a LEC representing a particular node and the LES. Moreover, such method and apparatus may be applicable to any switched network environment.